My aunt has ovarian cancer stage 4. Recently her cancer has metastasized to her vertebrae which has led to compression fracture of her vertebrae. She has severe pain in her back and has been asked bed rest all the time. Her doctor has started her on radiation therapy. She is now taking about a minute of radiation pulses everyday. She has undergone about 8 days of radiation. Her back pain has not subsided. I read somewhere that she should undergo vertebroplasty before the radiation, but her doctor says that there is no need for it. Is vertebroplasty absolutely essential, can her spine become fine with radiation. She is 47 years old.

This Medscape, article, "Vertebroplasty in Metastatic Spinal Disease," by neurosurgeon Dr.Julie G. Pilitsis, seems to confirm what you are suspecting:

When vertebroplasty is performed in conjunction with radiotherapy, most groups recommend that vertebroplasty be undertaken prior to radiation treatment for best results.[6,8,17] Murray, et al.,[22] have demonstrated that radiotherapeutic treatment of neoplasms is not affected by the presence of cement, nor is cement affected by radiation.

You might want to follow the link, print out the article and show it to your aunt's doctor.

However, this may be reassuring:

In a study reported by Weill, et al.,however, all patients in whom vertebroplasty was performed after radiotherapy failed to resolve pain experienced clear or moderate improvement.

Also, from the American College of Radiology web site, here's an FAQ on vertebroplasty.